Cathodic protection systems for marine devices are well known and various configurations of anodes and reference electrodes have been tried. For example, U.S. Pat. No. 3,853,730 to Anderson teaches separate anode and reference electrode configurations for mounting on the hull of a boat to provide cathodic protection for an outboard motor or stern drive propulsion unit attached to the boat. These anodes and electrodes are suitable for use in a cathodic protection system such as that disclosed U.S. Pat. No. 4,322,633 to the present inventor. As with all known systems, the reference electrode must be mounted a substantial distance from the anode to provide an appropriate reference signal indicative of the potential of the protected unit, thus generally necessitating mounting the electrodes on the boat remote from the propulsion unit.